The invention relates to a reference circuit, such as a reference circuit that provides a reference voltage and/or a reference current, for example.
Quite often a circuit may use a reference voltage that is different from available power supply voltage(s). As a result, the circuit may be coupled to another circuit, called a voltage reference circuit, that converts one or more of the available power supply voltage(s) into the desired reference voltage. For example, referring to FIG. 1, a voltage reference circuit 4 may include a resistor divider that is formed from resistors 1 and 2 that are serially coupled together between a positive power supply voltage (called V.sub.DD) and a negative power supply voltage (called V.sub.SS). In this manner, an output terminal 3, formed from the union of the two resistors 1 and 2, may provide a reference voltage (called V.sub.REF) that has a voltage level somewhere between the V.sub.DD and V.sub.SS power supply voltages.
Assuming that a load that is coupled to the output terminal 3 sinks/sources negligible current, certain circuit applications may benefit from using the voltage reference circuit 4. For example, it may be desirable for the V.sub.REF reference voltage to vary proportionately with changes in the levels of the V.sub.DD and V.sub.SS supply voltages, a feature that is inherent in the resistor divider topology of the voltage reference circuit 4. Furthermore, the resistor divider topology of the voltage reference circuit 4 permits the level of the V.sub.REF reference voltage to be substantially low, such as a voltage level in the range of approximately 0.2 to 0.9 volts, for example. The V.sub.REF reference voltage may also vary little with a temperature of the voltage reference circuit 4 because a temperature-induced change in the resistance of the resistor 1, 2 is matched by a proportionate change in the resistance of the other resistor 1, 2.
Unfortunately, the resistors 1 and 2 may dissipate excessive power, and as a result, a voltage reference circuit having a different topology may be used. For example, a bandgap voltage reference circuit (not shown) typically dissipates less power. The bandgap voltage reference circuit typically includes one or more p-n junctions that are connected in a manner to provide a reference voltage that varies little with temperature. However, unfortunately, the reference voltage that is provided by the bandgap voltage reference circuit may not vary with the supply voltage(s), the bandgap voltage reference circuit may not produce low reference voltages (e.g., voltages from 0.2 to 0.8 volts), and non-ideal characteristics of the p-n junctions may affect the circuit's performance.
Thus, there is a continuing need for a reference circuit that addresses one or more of the above-stated problems.